The invention relates to retroreflective articles and other articles useful for various applications, such as graphic designs and retroreflective products.
Articles containing polymer films have wide utility in such applications as commercial graphics for advertising and for retroreflective products. Specifically, retroreflective products (e.g., bead-based and prismatic-type (e.g. cube corner) retroreflective sheeting) have been developed to provide increased safety, especially during periods of reduced visibility. These articles may encounter demanding environments, such as extremes in temperature, chemical challenges from atmospheric pollution and road salt, and photo-reaction involving infrared, visible, and ultraviolet radiation from sunlight.
Polymers used for these articles should preferably achieve a high performance in order to withstand such conditions. Examples of prior polymers commonly used for making various articles are polyvinyl chloride (PVC), fluoropolymers, acrylics, and polyurethane.
Multilayer films containing the prior polymers have also been used in various articles. Such prior multilayer films also have had disadvantages. For example, certain prior multilayer films (which usually have had only two layers) may not be sufficiently flexible, may delaminate, or may be too expensive for commercial use.
Substitutes for these prior polymers or multilayer films would be desirable in order to avoid the above disadvantages. Thus, there are unmet needs for inexpensive polymer films that exhibit high performance (such as flexibility), are simple to make, and are environmentally friendly.
The present invention provides retroreflective articles that comprise a plurality of retroreflective elements; and a substantially continuous, substantially contiguous multilayer film having at least one layer of a urethane polymer and a core layer of a copolymer of alkylene (e.g., ethylene) and at least one non-acidic, polar co-monomer. The retroreflective elements may comprise transparent beads cooperating with a reflective coating or microstructured prism elements.
The present invention also provides novel multilayered films of contiguous layers including at least one layer of a urethane polymer and a core layer of a copolymer of alkylene and at least one non-acidic, polar comonomer. Novel methods of making such films are also disclosed.
In one embodiment, the core layer of an alkylene copolymer is formed from ethylene monomer and at least one non-acidic co-monomer selected from at least one of vinyl acetate, acrylate, and carbon monoxide. Typically, the ethylene copolymer comprises between 55 and 95 weight percent ethylene; and between 5 and 40 weight percent non-acidic co-monomer. If desired, the alkylene copolymer may further comprise an acidic or anhydride based co-monomer, typically less than about 10 weight percent of an acidic co-monomer.
Particularly preferred ethylene copolymers for use in the multilayered films of the present invention include: ethylene vinyl acetate (xe2x80x9cEVAxe2x80x9d), acid-modified EVA, anhydride-modified EVA, acid-acrylate-modified EVA, anhydride-acrylate-modified EVA, ethylene ethyl acetate (xe2x80x9cEEAxe2x80x9d), ethylene methyl acetate (xe2x80x9cEMAxe2x80x9d), acid- or anhydride-modified ethylene acrylate (xe2x80x9cAEAxe2x80x9d), ethylene/vinyl acetate/carbon monoxide copolymer (xe2x80x9cEVACOxe2x80x9d), ethylene/n-butyl acrylate/carbon monoxide copolymer (xe2x80x9cEBACOxe2x80x9d), and ethylene/n-butyl acrylate copolymer (xe2x80x9cEnBAxe2x80x9d).